Influence Of Different Operating Conditions Research Articles

Experimental and analytical study on an air-cooled single effect LiBr-H2O absorption chiller driven by evacuated glass tube solar collector for cooling application in residential buildings

Solar cooling turns out to be a feasible method to reduce the electricity consumption of air conditioning systems in buildings. Air-cooled single effect LiBr-H2O absorption chiller has shown advantages in residential applications. It can be driven by common evacuated tube solar collectors, and save water, maintenance expense and space, due to the absence of cooling tower. However, there is no available small capacity commercial air-cooled LiBr-H2O absorption chiller yet, because of the crystallization risk under ambient conditions. In this work, an air-cooled single effect absorption chiller for which the cooling capacity is 6kW and a solar air conditioning system were developed. The air-cooled single effect absorption chiller was fabricated and tested under a broad range of steady-state conditions. The chiller was proved successful for real application without crystallization risk and the influence of different operating conditions was also analyzed. Moreover, the performance of a solar air conditioning system using the proposed chiller was investigated for residential cooling application. The results show that the studied absorption chiller can meet about 65% of the total cooling load of the building with an average COPth of about 0.61. Furthermore, 28% of the titled solar radiation is converted into cooling capacity by the solar air conditioning system.

Microfluidic-assisted nanoprecipitation of antiviral-loaded polymeric nanoparticles

The chemical treatment called “chemotherapy of plants” consists in the in vivo administration of substances able to interfere with viral replication. The current availability of synthetic molecules with a high chemotherapeutic index, i.e. with a high ratio between the maximum concentration tolerated and the minimum effective, together with the possibility to further widen the therapeutic window by the use of appropriate nanocarriers, seems to open on the application level of a novel chemical approach to treat plant viral infections. Ribavirin, for example, is a synthetic water-soluble nucleoside that possesses broad spectrum activity against a variety of DNA and RNA plant viruses. As well known, water-soluble drugs are generally difficult to encapsulate in solid particles. Chemical modification of these drugs, such as esterification, may increase their encapsulation efficiency, but may also decrease bioactivity. In this work we have synthesized stable solid monodispersed PLGA (poly-d,l-lactic-co-glycolic acid) NPs with diameters ranging from 50 to 200nm containing ribavirin by using a microfluidic reactor with a flow-focusing geometry. Previous work carried out in our lab showed an improvement of drug loading efficiency when using a microfluidic approach in comparison with traditional nanoprecipitation methods for nanoencapsulation. On this basis we optimized Ribavirin loading within PLGA NPs by investigating the influence of different operating conditions, such as polymer concentration, flow rate ratio, τmix, microreactor-focusing channel diameter and length, on nanoparticle size and morphology. NPs characterization was performed by Dynamic light scattering (DLS) measurements and by scanning electron microscopy (SEM). The synthesized NPs showed a significant drug loading efficiency.

LES-DEM investigation of the time-related solid phase properties and improvements of flow uniformity in a dual-side refeed CFB

A parallel simulation of the gas-solid motions in a 3-D full-loop dual-side refeed circulating fluidized bed (DRCFB) is carried out by using Large-eddy Simulation coupled with Discrete Element Method (LES-DEM), in which the gas and the solid motions are solved under the Eulerian and the Lagrangian frames, respectively. The start-up flow patterns, the time-related solid phase properties about solid cycle time and solid residence time (SRT) distributions, and the improvements of gas-solid flow uniformity are explored. Furthermore, the influences of different operating conditions on the time-related solid phase properties are discussed. The results demonstrate that the transient pressure drop is a criterion for determining steady state in the start-up process and the fluctuations under different superficial velocities differ. The solid cycle time and the SRT distribution curves show a feature of early peak with an extended tail, which indicates that the solid flow exhibits a back-mixing phenomenon. The averaged solid cycle time in the whole system and the averaged SRTs in the three components (i.e., riser, cyclone, and dipleg) show distinct characteristics under different operating conditions. Moreover, nearly 70% of the solid cycle time elapses in the riser and 25% of that elapses in the dipleg while only 5% of that elapses in the cyclone. Finally, the dual-side refeed structure remarkably improve the gas-solid flow uniformity (i.e., homogenous) in the DRCFB riser, especially in the inlet and outlet regions.

Droplet synthesis of silver nanoparticles by a microfluidic device

Silver nanoparticles are synthesized by the reduction of metal salt solutions from sodium borohydride in a microfluidic chip. The influence of different operating conditions on silver particle diameter, morphology, size distribution, and elemental compositions has been investigated. The results demonstrated that ethylenediaminetetraacetic acid (EDTA) serving as a complexant significantly affected the particle size of synthesized silver nanoparticles. An increase in the silver nanoparticle mean diameter was observed with decreasing NaBH4/AgNO3 molar concentration ratios, and increasing fluid flow rates.

The Influence of Different Operating Conditions on the Blood Damage of a Pulsatile Ventricular Assist Device.

Because of pulsatile blood flow's benefit for myocardial recovery, perfusion of coronary arteries and end organs, pulsatile ventricular assist devices (VADs) are still widely used as paracorporeal mechanical circulatory support devices in clinical applications, especially in pediatric heart failure patients. However, severe blood damage limits the VAD's service period. Besides optimizing the VAD geometry to reduce blood damage, the blood damage may also be decreased by changing the operating conditions. In this article, a pulsatile VAD was used to investigate the influence of operating conditions on its blood damage, including hemolysis, platelet activation, and platelet deposition. Three motion profiles of pusher plate (sine, cosine, and polynomial), three stroke volumes (ejection fractions) (56 ml [70%], 42 ml [52.5%], and 28 ml [35%]), three pulsatile rates (75, 100, and 150 bpm), and two assist modes (copulsation and counterpulsation) were implemented respectively in VAD fluid-structure interaction simulations to calculate blood damage. The blood damage indices indicate that cosine motion profile, higher ejection fraction, higher pulsatile rate, and counterpulsation can decrease platelet deposition whereas increase hemolysis and platelet activation, and vice versa. The results suggest that different operating conditions have different effects on pulsatile VAD's blood damage and may be beneficial to choose suitable operating condition to reduce blood damage in clinical applications.

Absorption of Sulfur Dioxide with Sodium Hydroxide Solution in Spray Columns

The absorption of sulfur dioxide into highly concentrated sodium hydroxide in a spray column from simulated flue gas was investigated. The influences of different operating conditions on the SO2 removal efficiency, such as sodium hydroxide concentration, liquid-to-gas ratio, gas velocity and SO2 concentration, were examined. The overall volume transfer coefficients (kGa), under moderate conditions, were obtained by introducing the instantaneous and irreversible chemical reaction into the two-film theory to establish a model that allowed the calculation of theoretical values of the overall volume-transfer coefficient. It was found that the absorption process was controlled by diffusion through gas film when a highly concentrated caustic soda solution was adopted. The overall volume-transfer coefficient was essentially independent of concentration of SO2 in gas phase and positively related to the gas and liquid flow rates. The formula of kGa was fitted for the process and found to be in good agreement with ...

Assessment of biogas production from MBT waste under different operating conditions

In this work, the influence of different operating conditions on the biogas production from mechanically–biologically treated (MBT) wastes is investigated. Specifically, different lab-scale anaerobic tests varying the water content (26–43% w/w up to 75% w/w), the temperature (from 20 to 25°C up to 55°C) and the amount of inoculum have been performed on waste samples collected from a full-scale Italian MBT plant. For each test, the gas generation yield and, where applicable, the first-order gas generation rates were determined. Nearly all tests were characterised by a quite long lag-phase. This result was mainly ascribed to the inhibition effects resulting from the high concentrations of volatile fatty acids (VFAs) and ammonia detected in the different stages of the experiments. Furthermore, water content was found as one of the key factor limiting the anaerobic biological process. Indeed, the experimental results showed that when the moisture was lower than 32% w/w, the methanogenic microbial activity was completely inhibited. For the higher water content tested (75% w/w), high values of accumulated gas volume (up to 150Nl/kgTS) and a relatively short time period to deplete the MBT waste gas generation capacity were observed. At these test conditions, the effect of temperature became evident, leading to gas generation rates of 0.007d−1 at room temperature that increased to 0.03–0.05d−1 at 37°C and to 0.04–0.11d−1 at 55°C. Overall, the obtained results highlighted that the operative conditions can drastically affect the gas production from MBT wastes. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of disposed waste, the presence and type of temporary and final cover systems.

Electrochemical performance modeling of a proton exchange membrane electrolyzer cell for hydrogen energy

This paper presents a comprehensive computational model for the proton exchange membrane (PEM) electrolyzer cells, which have attracted more attention for renewable energy storage and hydrogen production. A new ohmic loss model of a PEM electrolyzer cell has been developed and the influence of different operating conditions and physical design parameters on its performance has been investigated, including operating temperature, pressure, exchange current density, electrode thickness, membrane thickness and interfacial resistance. The interfacial resistance between the membrane and electrode has been found to play an important part for electrolyzer performance and an overpotential is increased significantly with the interfacial resistance. At a current density of 1.5 A/cm2, the performance loss due to the interfacial resistance between the membrane and electrode comprises 31.8% of the total ohmic loss. Thickness changes in either electrode or membrane also have significant impacts on the electrolyzer performance mainly due to their contributions to the diffusion overpotential and ohmic loss. Increasing the operating temperature will result in lower electrolyzer overpotential, while increasing the operating pressure will lead to higher electrolyzer overpotential, which is mainly controlled by the open circuit voltage. Results obtained from the present model will provide a comprehensive understanding of design parameter effects and consequently improve the design/performance in a PEM electrolyzer cell.

Influence of process parameters on the performance of an oxygen blown entrained flow biomass gasifier

Abstract Pressurized, O 2 blown, entrained flow gasification of pulverized forest residues followed by methanol production is an interesting option for synthetic fuels that has been particularly investigated in the Nordic countries. In order to optimize gasification plant efficiency, it is important to understand the influence of different operating conditions. In this work, a pressurized O 2 blown and entrained flow biomass gasification pilot plant was used to study the effect of four important process variables; (i) the O 2 stoichiometric ratio ( λ ), (ii) the load of the gasifier, (iii) the gasifier pressure, and (iv) the fuel particle size. Commercially available stem wood fuels were used and the process was characterized with respect to the resulting process temperature, the syngas yield, the fuel conversion and the gasification process efficiency. It was found that CH 4 constituted a significant fraction of the syngas heating value at process temperatures below 1400 °C. If the syngas is intended for catalytic upgrading to a synthetic motor fuel where CO and H 2 are the only important syngas species, the process should be optimized aiming for a process temperature slightly above 1400 °C in order to reduce the energetic losses to CH 4 and C 6 H 6 . This resulted in a cold gas efficiency (based only on CO and H 2 ) of 70%. The H 2 /CO ratio was experimentally determined within the range 0.45–0.61. Thus, the syngas requires shifting in order to increase the syngas composition of H 2 prior to fuel synthesis.

Ultrasonic-assisted extraction of anthraquinones from Heterophyllaea pustulata Hook f. (Rubiaceae) using ethanol–water mixtures

In this study, ultrasound-assisted extraction (UAE) was evaluated as an easier and more efficient alternative method for the isolation of anthraquinones (AQs) from Heterophyllaea pustulata Hook f. (Rubiaceae), compared with conventional extraction techniques. The extraction was performed using an ethanol–water solution as solvent. The influence of different operating conditions, as temperature, time, solvent composition, and solvent/sample ratio and its relationship with ultrasonic techniques was analyzed. For this purpose and to achieve global optimization of the ultrasound-assisted extraction of H. pustulata, Taguchi experimental design with a L9 orthogonal array was applied.The results showed that the yield obtained with the ultrasound assisted extraction is approximately twice higher than the traditional Soxhlet technique, and Taguchi analysis demonstrated that the most influential factor is solvent concentration, followed by time, temperature, and solvent/sample ratio. The solvent composition effect is directly related to cavitation process, and the effect of solvent physical properties on it. The optimal combination of these factors on the ultrasound assisted extraction is a solvent composition 60% v/v of ethanol, a solvent/sample ratio equal to 20:1, a temperature of 55°C, and an extraction time of 30min.

Experimental Assessment of Water Sprays Utilization for Controlling Hydrogen Sulfide Releases in Confined Space

This paper reported the utilization of water spray for controlling H2S release in a confined space, which is especially important in industry. A typical spray tower was modified to simulate the confined space for people's enterable routine operation (e.g., pump room), in which the dilution capacity of water sprays can also be evaluated. This work consists of two parts: the first part focuses on the influences of different operating conditions on chemical dilution capacities of water sprays in mechanisms; the second one is comparison between two nozzle configurations for evaluating their feasibilities of practical application. Water sprays express eligible performance for H2S release control even though their dilution capacity was weakened at high gaseous concentrations and rates of releases. The presence of Na2CO3can significantly improve absorption effectiveness of H2S in water and the optimal Na2CO3additive was found to be 1.0 g·L−1in this test. Compared with Na2CO3, adjusting water flow rate may be an effective strategy in enhancing dilution capacity of water sprays due to the fact that larger flow rate led to both less dilution time (TD) and dilution concentration (CD). Furthermore, multinozzle configuration is more efficient than single-nozzle configuration under the same water consumption.

Sub-Synchronous Interaction Damping Control for DFIG Wind Turbines

This paper presents a damping control to mitigate sub-synchronous interactions (SSI) in doubly-fed induction generator (DFIG) wind turbines connected to series-compensated lines. This issue has gained attention due to the recent SSI phenomena reported in DFIG wind farms located near series capacitors. Two approaches which add a supplementary damping control signal are compared: one of them, integrated to the grid-side converter, and the other one, to the rotor-side converter. The SSI damping controls are designed using a multi-input multi-output state-space methodology. This allows to easily tune a high performance controller using several measurements and control inputs. Small- and large-signal stability analyses, robustness aspects, impact of the supplementary controls on the system modes, and influence of different operating conditions on the SSI are also discussed. The obtained results show that the supplementary control is able to properly damp the sub-synchronous oscillations of DFIG wind turbines by updating the existing DFIG control systems without the inclusion of expensive additional damping devices, and reducing the risk of wind generation tripping.

Co-production of hydrogen and carbon nanofibers from methane decomposition over zeolite Y supported Ni catalysts

The objective of this paper is to study the influences of different operating conditions on the hydrogen formation and properties of accumulated carbon from methane decomposition using zeolite Y supported 15% and 30% Ni, respectively, at a temperature range between 500 and 650°C in a pilot scale fixed bed reactor. The temperature ramp was showed a significant impact on the thermo-catalytic decomposition (TCD) of methane. An optimum temperature range of 550–600°C were required to attain the maximum amount of methane conversion and revealed that at 550 and 600°C, catalyst showed longer activity for the whole studied of experimental runs. Additionally, at 550°C, the methane decomposition is two times longer for 30% Ni/Y zeolite than that for 15% Ni/Y zeolite catalyst, whereas it is almost three times higher at 500°C. A maximum carbon yield of 614.25 and 157.54gc/gNi were reported after end of the complete reaction at 600°C with 30% and 15% Ni/Y zeolite catalyst, respectively. From BET, TPD, and XRD analysis, we had reported that how the chemistry between the TCD of methane and metal content of the catalysts could significantly affect the hydrogen production as well as carbon nano-fibers. TEM analysis ensured that the produced carbon had fishbone type structures with a hollow core and grew from crystallites of Ni anchored on the external surface of the catalysts and irrespective of the metal loadings, the whisker types of nano filaments were formed as confirmed from FESEM analysis. Nevertheless, the effect of volume hourly space velocity (VHSV) on the methane conversion was also investigated and reported that the methane conversion increased as VHSV and nickel concentration in Ni–Y catalysts increased. Additionally, the initial methane decomposition rate increases with VHSV and it has reverse and non-linear relevancy to the weight of Ni/Y zeolite catalyst.

Granular mixing optimization and the influence of operating conditions in a double screw mixer

Granular mixing processes often seek a high degree of homogeneity and, in some instances, can influence simultaneous processing, such as chemical reactions and heat and/or mass transfer. However, specific operating conditions and differences in particle size, shape, and/or density lead to segregation and reduce the mixing effectiveness of these processes. In this study, red oak chips and glass beads are mechanically mixed using a laboratory-scale double screw mixer and the mixing effectiveness is evaluated under various operating conditions. Qualitative optical visualization from four spatially aligned and temporally synced projections is combined with quantitative composition and statistical analysis techniques to optimize and investigate the influence of different operating conditions on the mixing effectiveness of the screw mixer. For the parameters considered in this study, the best mixing performance occurs when the screw rotation speed is ω=60rpm, the dimensionless screw pitch is p/D=1.75, the screw rotation orientation is counter-rotating down-pumping, and the material injection configuration features the red oak chips and glass beads injected into port one and two, respectively.

Optimization of the Continuous Polycondensation Process for Polyethylene Adipate

A continuous polycondensation process for polyethylene adipate in a bubbling reactive distillation tower with six trays allowed achieving high conversion of carboxyl end groups within short residence times. Influences of different operating conditions including residence time, reaction temperature, pressure, etc. on reactor performance were investigated by experimental and simulation analyses. Optimal conditions for polyethylene adipate continuous polycondensation in the bubbling reactive distillation tower reactor were defined and applied to the process.

Optimization of bubble column performance for nanoparticle collection

Fibrous media embody the most effective and widely used method of separating ultrafine particles from a carrier fluid. The main problem associated with them is filter clogging, which induces an increasingly marked pressure drop with time and thus imposes regular media cleaning or replacement. This context has prompted the idea of investigating bubble columns, which operate at constant pressure drop, as alternatives to fibrous filters. This study examines the influence of different operating conditions, such as liquid height, air flow rate, bubble size and presence of granular beds on ultrafine particle collection. Experimental results show that bubble columns are characterised by high collection efficiency, when they feature a large liquid height and small diameter bubbling orifices, while their efficiencies remain lower than those of fibrous filters. Gas velocity does not greatly influence collection efficiency, but the inclusion of a granular bed, composed of beads, increases the bubble residence time in the column, thereby increasing the column collection efficiency.

Study on Influencing Factors of Rapid Identification of Drainage Oil by Conductivity Method

Study on influencing factors of rapid identification of drainage oil by conductivity method through experimental, discuss the influence of different operating conditions on the determination results. The effects of oil/water ratio, oscillation time, temperature, and oil type on conductivity were explored. Measured water conductivity of different kinds of oil, analysed the change of the conductivity and the best operating conditions were elected. The results showed that under the condition of normal temperature, shocked the mixture for 30s, the oil/water ratio was 4:1 and subsided for 15 minutes,the conductivity of drainage oil,frying oil and edible oil were 72.7 us/cm34.3us/cm12.5us/cm. The conductivity was largest and the testing results was most sensitive.

Influence of operating conditions on the optimum design of electric vehicle battery cooling plates

The efficiency of cooling plates for electric vehicle batteries can be improved by optimizing the geometry of internal fluid channels. In practical operation, a cooling plate is exposed to a range of operating conditions dictated by the battery, environment, and driving behaviour. To formulate an efficient cooling plate design process, the optimum design sensitivity with respect to each boundary condition is desired. This determines which operating conditions must be represented in the design process, and therefore the complexity of designing for multiple operating conditions. The objective of this study is to determine the influence of different operating conditions on the optimum cooling plate design. Three important performance measures were considered: temperature uniformity, mean temperature, and pressure drop. It was found that of these three, temperature uniformity was most sensitive to the operating conditions, especially with respect to the distribution of the input heat flux, and also to the coolant flow rate. An additional focus of the study was the distribution of heat generated by the battery cell: while it is easier to assume that heat is generated uniformly, by using an accurate distribution for design optimization, this study found that cooling plate performance could be significantly improved.

Neural network modeling the effect of oxygenate additives on the performance of Pt–Sn/γ-Al2O3 catalyst in propane dehydrogenation

The effect of oxygenate additives, water and methanol, to the feed on the performance of industrial Pt–Sn/γ-Al2O3 catalyst in dehydrogenation of propane was studied by neural network modeling. Because of the complex nature of the system and very low levels of oxygenate addition, neural networks were employed as an efficient and accurate tool to obtain the behavior of the system. Dehydrogenation reaction was carried out in a fixed-bed quartz reactor in the temperature range of 575–620 °C. Steady state modeling was performed in three different levels of oxygenate addition, and conversion and selectivity at different levels. The optimum amounts of water and methanol for reaction temperatures of 575, 600 and 620 °C were found to be 83.60, 125.40 and 139.34 ppm, respectively, for water and 9.98, 24.94 and 49.88 ppm for methanol by neural network method. The neural network-based optimum was compared with that obtained from experimental data. In this case, various architectures have been checked using 70 % of experimental data for training of artificial neural network (ANN). Among the various architectures multi layer perceptron network with trainlm training algorithm was found as the best architecture. Temperature and water or methanol amount for the present constituents in the feed were network input data. Output data were conversion, selectivity to propylene and yield of propylene. Comparing the obtained ANN model results with 30 % of unseen data confirms ANN excellent estimation performance. The influence of different operating conditions on the accuracy of the results was also investigated and discussed. The propylene yields, however, passed a maximum at the optimum levels of oxygenates coincided with a substantial reduction of coke formation as well. The modeling results were accurate with <0.9 % error.

Damage and Failure of Silver Based Ceramic/Metal Joints for SOFC Stacks

AbstractThe increasing interest in lightweight solid oxide fuel cell (SOFC) systems for mobile applications has raised the awareness for questions concerning mechanical robustness of sealing materials in thermo‐cyclic operation. In the planar SOFC design considered in the current work, a metallic silver based braze sealant is used. Although, these rather ductile metallic seals are considered to have advantages compared to brittle glass ceramics under thermal cycling conditions, the behavior of such sealant materials after application relevant thermal cyclic operation has not been reported so far. Hence, the post‐operational characterization of a series of silver braze sealed stacks operated isothermally and under thermal cycling conditions is reported with particular emphasis on the braze morphology. The stacks were disassembled after operation, specimens were extracted in various characteristic positions, and metallographically prepared cross‐sections were analyzed by optical and electron microscopy. It was observed that micro‐pores were formed in the sealant that terminated stack operation, and that the extent of this porosity depended on the actual operation conditions leading eventually to leakage and in some cases even to melting effects. The discussion of the results focuses on the influence of different operation conditions on the damage progress and failure of silver based braze joints.